U.S. Pat. No. 4,875,660 issued in 1989 to the inventors Pierre GAGNON and Pierre LAFOREST (the inventor of the present invention), hereafter the “Gagnon patent” which is hereby incorporated to the present specification by way of reference, shows a push actuator to be used as a pushing device, for example instead of a hydraulic cylinder. The push actuator of the Gagnon patent has the advantage of requiring less space than conventional hydraulic cylinders when in a contracted position, due to the fact that no concentric column portions have to be stored within each other. Also, it can support very heavy loads, since it forms a cylindrical column when in an extracted position, without any concentric portions as with a hydraulic cylinder, and this vertical structure has a high vertical rigidity in compression. Very important world-wide commercial success of the push actuator of the Gagnon patent has proven it to be a very advantageous alternative to conventional hydraulic cylinders.
The Gagnon push actuator generally works as follows. A hollow cylindrical rotor is rotatably carried over a base fixed to the ground. A motor selectively activates the rotor. A first horizontal band is vertically stacked in a helix and rests on the ground, while a second vertical band is horizontally stacked in a spiral, the latter located in an annular magazine located co-axially around the rotor. The upper end of each band is fixedly attached to a load-bearing platform. When the rotor is rotated, each turn of the vertical band is guided and installed in helical configuration between two vertically successive turns of the horizontal band, to thus gradually form a vertical telescopic column. The load of the platform supported by the push actuator is induced through the vertical and horizontal band turns which rest on each other, and then to idle rollers provided on the rotor which support the horizontal band.
One problem associated to the push actuator of the Gagnon patent is that the horizontal and vertical bands simply rest on each other without being interlocked in any way. This is not problematic when a load is applied on the push actuator platform both axially and in compression, since the push actuator has a very important vertical load-bearing capacity. However, the structural integrity of the column is likely to be compromised if a force is exerted on the column perpendicularly to its central axis. Indeed, in such a case, the two intertwined bands of the column may accidentally disengage themselves from one another, which would lead to the column collapsing. To circumvent this problem, the push actuator of the Gagnon patent is usually used together with guiding devices, such as scissor-type linkages, that prevent lateral movement of the load carried by the push actuator. Indeed, the scissor-type linkages will only allow the load being carried to be moved in the direction of the axis of the push actuator. Also, it can be seen that the vertical column of the Gagnon push actuator may not be submitted to any type of tension force, since once again the two intertwined bands would disengage themselves from each other and the column would collapse.